PT674720E - COLD MODELED RESISTANCE CANE ACOUSES - Google Patents

Abstract

A method of making high-strength steel parts is disclosed by providing a blank of high-strength steel having a ferrite-pearlite microstructure and high-strength mechanical properties and cold forming the blank by upsetting, forging, or extrusion to provide a part having a desired geometric configuration while the mechanical strength of the part remains substantially the same or greater than the blank.

Description

1

Description "Cold-formed high strength steel parts"

FIELD OF THE INVENTION The present invention relates to a process for the manufacture of high strength steel parts and, more particularly, relates to a process in which a high strength high strength steel part is cold molded to obtain a part having a desired geometric configuration so that the strength of the part remains substantially equal to or greater than that of the blank.

Background of the invention

So far, a number of processes have been used for the fabrication of steel parts. These processes often use cold forming techniques, such as splicing, bending and extrusion, which are well known to those skilled in the art. In creping, the cross-sectional area of part or all of the initial metal part is increased. The header is a particular form of scoring, wherein the blank is a wire or bar stock. Screw heads are often made using the header techniques. In extrusion, the initial metal member is forced through the bore of a die with a desired cross-sectional shape to produce a segment of uniform cross-section.

One such process for manufacturing high strength steel parts, which is well known, begins by annealing or softening the initial steel part by another process. The annealed initial steel part is then cold formed, in a process which is included in one of the above-mentioned type-shaping techniques, to obtain the desired geometrical configuration. The piece, now shaped, is then subjected to heat treatment, i.e., is austenitized, quenched by quenching and tempering, to obtain the desired high strength mechanical properties. The steel material of the resulting part has a welded martensite microstructure. The mechanical properties produced by such heat treatments are often inconsistent and may vary from piece to piece. In addition, the annealing and heat treatment steps significantly increase the costs of the overall process for the fabrication of high strength steel parts, due in large part to the energy consumption which is associated with the heating of the part.

In another process for the manufacture of high strength steel parts, the initial steel part is initially austenitized, quenched by rapid quenching and then subjected to tempering to a point where the mechanical properties of the initial part after heat treatment are such that the blank could then be cold formed in a process which includes one of the three above-mentioned modeling techniques to obtain the desired geometric configuration. The steel material of the finished part obtained by this process has a non-annealed martensitic microstructure. Although this process apparently has advantages over the previously described process in that, as stated, the tolerances of strength from one part to another are tightened, which can be obtained with this process, however, it still uses a costly heat treatment process. It is known the process of cold modeling initial pieces of high strength material. In U.S. Patent 3,904,445, assigned to the inventor of the present invention, there is provided a method for cold modeling a segment of high strength steel bar material to obtain a U-bolt. The '445 patent discloses such a 3 length of the bar material made from a steel material having a composition consisting essentially of, in weight percent: carbon, between about 0.50 and 0.55%, manganese between about 1.20 and 1.65 %, vanadium between about 0.03 and 0.05%, with the remainder consisting substantially all of iron. However, cold forming of a fold in a segment of bar material is less severe than other cold forming techniques, such as pealing and extrusion. Until now it has generally been thought that the cold molding of a high strength initial part to obtain a part by extrusion or extrusion techniques would result in the formation of cracks, or even fractures, in the piece of finished high strength steel or at least it would be probable to require the gradual formation of the part by a series of cold forming steps with a step of annealing or reducing the stresses effected between cold forming operations. Such cracks or fractures would probably lead to the ruin of the piece. In addition, the use of such cold forming and annealing increases the time and costs for the fabrication of such high strength steel parts. GB 1 535 775 describes a process for the production of cold-formed parts having a tensile strength of at least 750 N / mm 2 and a yield point of more than 600 N / mm 2 from a bar or a wire of steel, with or without a low alloy, with a tensile strength of more than 500 N / mm2 in the condition of sweet annealing or rolling. The steel is cold-worked by stretching, and then extruded by compression, in the opposite direction to stretching. The steel comprises carbon, at most 0.6%, silicon, manganese, sulfur and, for example, chromium, the remainder being iron. German patent DE 3 434 743 discloses a process for the production of 477 parts of machines by hot rolling of steel at a temperature of 800 ° C to 1150 ° C and then a controlled cooling operation. The cooled and rolled bars can then be finished by a cold forming process to shape or tighten the edges of the edges. U.S. Patent 4,289,548 describes a process for the production of high strength steel bars by subsequent cold drawing. Vanadium-containing steel hot rolled bars are made stronger by subsequent cold drawing. An advantage of the process is, as stated, only light traction is required.

A process for the manufacture of a finished high-strength steel part according to the invention comprises the steps of providing an insert of high strength steel material with a ferrite-perlite microstructure and a deformation resistance of at least 621 N / mm2 (90,000 psi), a tensile strength of at least 827 N / mm2 (120,000 psi) comprising: by weight: carbon 0.30 to 0.65% manganese 0.30 to 2, 5% at least one grain refining element from the group consisting of aluminum, cell, titanium and vanadium and mixtures thereof in an amount of 0.03 to 0.35%. iron the remainder and cold mold the blank at room temperature by creping or forging to provide the finished part with the desired geometric configuration, the mechanical tensile and deformation properties of the workpiece, substantially equal to or greater than that of original part, and without the need for further processing steps to improve toughness. The term "blank", as used herein, has its usual meaning, i.e. a piece of metal to be cold formed, to obtain a finished piece with the desired geometrical configuration. The initial pieces include metal pieces, such as bar materials (i.e., a piece of steel having the length in proportion to its thickness). The term "cold forming", as used herein, has its usual meaning, i.e. a modeling operation done at ambient temperature. It is known to use aluminum, niobium, titanium and vanadium as grain refiners in the heat treatment at elevated temperature of the steel, being "ferrous grain refiners" a collective name for these specific elements. The present invention relates to a process for the manufacture of high strength steel parts from the initial pieces of high strength steel material with ferritic-pearlite microstructure and a tensile strength of at least 827 N / mm 2 (120,000 psi) and a deformation resistance of at least 621 N / ram2 (90,000 psi), with the following composition, in weight percent: carbon -0.30 to 0.65%, manganese - 0.30 to 2 , 5%, at least one grain refining element selected from the group consisting of aluminum, niobium (i.e., colloidal), titanium and vanadium and mixtures thereof in an amount of 0.03 to 0.35% and the remainder of iron , as set forth in claim 1. The present invention provides a process for the manufacture of high strength steel parts from starting parts by cold molding of the blank at room temperature using milling or forging techniques to provide a part with the config with the desired geometry of ferrite-perlite microstructure, so that the mechanical properties of tensile strength and tensile strength of the workpiece are substantially equal to or greater than those of the workpiece and in which the workpiece, with the desired mechanical properties of resistance tensile and deformation, is produced without the need for further processing steps to improve toughness.

Preferred embodiments are indicated in the secondary claims.

At least in part because of its geometrical configuration, some parts may require a reduction of stresses, in a temperature range from 232 ° C (450 ° F) to 649 ° C (1200 ° F), to raise, lower, or otherwise modify the physical characteristics of the steel part (for example tensile strength, creep resistance, percent elongation, hardness, percentage area reduction, etc.).

The principles of the present invention, its objects and advantages will be better understood with reference to the following detailed description.

DETAILED DESCRIPTION OF THE INVENTION The process of the present invention can be used for the production of a wide variety of finished high-strength steel parts, including bolts and screws of various types (U-bolts, eye bolts, J-bolts, hexagonal head screws, square head screws, etc.), shafts, camshafts, screws, oscillation resistant rods and others capable of modeling by the cold room temperature modeling process described herein.

In a preferred embodiment, the process of the present invention for the manufacture of high strength steel parts includes the provision of a high tensile steel stock blank 7 having a fine perlite microstructure in a ferritic matrix, at least 827 N / mm 2 (120 000 psi), and preferably at least 10 000 N / mm 2 (150 000 psi) and a deformation resistance of at least 627 N / mm 2 (90 000 psi) and preferably less 896 N / mm2 (130,000 psi). Perlite constituents are generally considered to be "fine" when their lamellae are not susceptible to definition with an optical magnification of 1000 times. In one embodiment, the high strength steel material used as a starting workpiece has been reduced and cold stretched to provide a workpiece with the above mechanical properties of tensile strength and deformation resistance. The high strength steel material used to manufacture the blank has the second composition, in percent by weight:

Carbon 0.30 to 0.65%

Manganese 0.30 to 2.5% at least one ferrous grain refiner from the group consisting of aluminum, niobium, titanium and vanadium and mixtures thereof in an amount of 0.03 to 0.35%.

Iron the rest.

According to a more preferred embodiment, the high strength steel material has the following composition, in percent by weight:

Carbon 0.50 to 0.55%

Manganese 1.20 to 1.65% at least one ferrous grain refiner, from the group consisting of aluminum, niobium, titanium and vanadium, and mixtures thereof, in an amount of from about 0.03 to 0.15%

Iron the rest.

Although aluminum, niobium (ie colundum), titanium and vanadium act as grain refiners, it is the most preferred vanadium of grain refiners. The blank, having a mechanical tensile strength and tensile strength and tensile strength composition as indicated above, is then cold formed using techniques such as creping or extrusion at room temperature to provide a workpiece with the desired geometric configuration so that the mechanical properties of tensile strength and deformation resistance of the workpiece are substantially equal to or greater than those of the workpiece. The molded part with the given tensile strength and deformation resistance properties is produced without the need for further processing steps, such as the final stress reduction step, to increase the toughness. However, for certain geometric configurations and certain applications of the part, a step of reducing the stresses may be necessary. The starting part of high strength steel material having a tensile strength of at least 800 N / mm2 (120,000 psi) and a strain resistance of at least 600 N / mm2 (90,000 psi) is used as process of the present invention and is produced by any suitable process known in the art. Such a process is disclosed in U.S. Patent 3,904,445. The '445 patent discloses a processing sequence for producing a high strength steel bar material particularly useful for the production of threaded connecting pieces, which include the U-bolts In the described process, the rod material% f produced has a fine grain structure between ASTM No 5-8. In the filed process, a steel having a chemical composition within certain limits is subjected to a standard heat reduction operation within the range of 10-15% of the final gauge. The hot reduced bar stock is then cut or separated into individual sections for rapid cooling through the air. Thereafter, individual portions of the hot reduced bar stock are subjected to a cold finish to the final gauge. The final step is a step of controlled reduction of the stresses, to increase the properties of mechanical resistance. This step of reducing stresses comprises heating the sections of bar material at a temperature of about 260-450Â ° C (500-850Â ° F) for about one hour, but may not be necessary. Thus, such bar material, with or without any reduction of stresses, can be used to model the initial piece of high strength steel. The following example illustrates the practice of the present invention for producing a hexagonal head bolt from high strength steel bar material produced in accordance with the process disclosed in the above-described U.S. Patent 3,904,445.

Example.

A high strength steel bar material equivalent to grade 8 resistance steel, having a diameter of 1.25 cm (1/2 "), was cut into approximately 10 cm (4") sections. This material has a tensile strength of at least 1 000 N / mm 2 (150 000 psi) and a deformation resistance of at least 900 N / mm 2 (130 000 psi), with a fine ferrite-perlite microstructure and a fine grain. One end of each length of the material was threaded using known threading processes, for example pressing, to provide the same 3.8 cm (1 1/2 ") of thread. With the length of bar material at or near ambient temperature, the hexagonal head of the screw was formed by header at one or more times at the other end of each length of bar stock with a hexagonal shaped die, using a mechanical forging pressing process, applying a pressure of approximately 150 tons. The hexagonal head of the resulting screw has a thickness of about 1 cm (3/8 ") and a width of about 2 cm (3/4"). The mechanical properties of tensile strength and deformation resistance of the hexagonal head screw product are substantially equal to or greater than those originally possessed by the bar material and therefore, no further reinforcing operations are required. The finished hex head bolt also has the desired mechanical ductility characteristic that the initial bar had, so no further processing steps are required to improve the toughness. However, for certain uses of the hexagonal head screw, a stress reduction operation may be required. For example, in some uses it is not desirable for a screw to undergo fracture under its head when subjected to a pull. Usually, it is most desirable for the threads to be the weakest point of the screw. In some cases, the reduction of stresses improves the tenacity of the screw so that it undergoes, under tensile stresses, on the threads.

Compared with those produced by the foregoing processes, which used a heat treatment process (i.e., austenitization, hardening by quenching and quenching), especially when the heat treatment was used after cold forming to produce the mechanical properties of high strength of the part, the finished parts made in accordance with the present invention are more likely to consistently have mechanical properties contained within narrower tolerance intervals. This position is confirmed by the results of mechanical strength tests performed on samples of hexagonal head screws produced by a method according to the present invention and on hexagonal head screws produced by a prior art process which includes a treatment process after cold forming. For example, a total of 50 heat treated, 1/2 "x 3 1/2" grade 8 hex head bolts had tensile strengths ranging from as low as 1,000 N / mm2 (150,000 psi) to values as high as 17216 psi (1 146 N / mm2), the average being 1 100 N / mm 2 (160 000 psi). On the other hand, 50 1/2 "x 3 1/2" hexagonal head 8 grade 8 bolts made in accordance with the present invention exhibited tensile strength values ranging from such low values such as 1 145 N / mm2 (166,000 psi) at values as high as 170,000 psi, an average value of 168,000 psi (1 160 N / mm2). Thus, with the present invention, it is more likely to consistently produce high strength steel metal parts within a narrower range.

Rua do Salitre, 395, r / c-Brt. 1250 LISBOA

Claims (7)

A process for the manufacture of a high strength steel part, which comprises the steps of providing an initial piece of high strength steel material with ferrite-perlite microstructure and a resistance to the deformation of the steel less than 621 N / mm2 (90,000 psi), a tensile strength of at least 827 N / mm2 (120,000 psi), which comprises, by weight: Carbon · 0.30 to 0.65% Manganese 0.30 to 2 , 5% at least one grain refining element from the group consisting of aluminum, niobium, titanium and vanadium and mixtures thereof in an amount of 0.03 to 0.35%. Iron the remainder and the cold molding of the blank at room temperature by gluing or drawing, to provide a part having a final shape with a desired geometric configuration, the mechanical properties of tensile strength and deformation resistance being of the part substantially equal to or greater than those of the blank, and without the need for further processing steps to improve toughness. A process according to claim 1, in which the high strength steel material has been previously reduced and cold drawn to provide the blank. A process according to any one of claims 1 or 2, wherein the high strength steel material blank has a tensile strength of at least 10 000 N / mm (150,000 psi) and a tensile strength. hair deformation / / / / / 2 minus 896 N / mm 2 (130,000 psi). A process according to any of the preceding claims, in which the high strength steel material comprises, in percent by weight: Carbon 0.50 to 0.55% Manganese 1.20 to 1.65% at least one refining element of the group consisting of aluminum, niobium, titanium and vanadium and mixtures thereof in an amount of 0.03 to 0.15% Iron the balance. A process according to any of the preceding claims, in which the initial piece of high strength steel material has a fine perlite microstructure in a ferritic matrix. A process according to any of the preceding claims in which the part with the mechanical characteristics is subjected to a reduction of the stresses, at a temperature in the range of 232 ° C (450 ° F) and 649 ° C (1200 ° F ) to modify the physical characteristics of the part. Method according to any of the preceding claims, in which the part is chosen from the group of parts formed by various types of threaded rods, screws, shafts and camshafts. Abstract: A process for the manufacture of high strength steel parts comprising the provision of a high strength steel blank having a ferrite microstructure -perlite and high strength mechanical properties, and the cold molding of the blank by splicing, forging or extrusion to provide a part with a desired geometric configuration while the mechanical strength of the part remains substantially equal to or greater than of the initial part. Lisbon, June 9, 2000